This study aimed to investigate the influence of aging on muscle thickness in lower limbs, with specific emphasis on the site- and gender-related differences. Subjects were a total of 191 healthy young and elderly persons of both genders : 51 young men (24.2±3.6 yrs), 45 young women (23.1±3.2yrs), 51 elderly males, and 44 elderly females. Lower leg anterior, and lower leg posterior muscle thickness was determined using a brightness mode ultrasonographic apparatus. At all sites except for the thigh posterior, the muscle thickness values were significantly greater in the young than in the elderly groups of both genders, even in terms of the ratio of muscle thickness to body mass^1/3 (Mt/Wt^1/3 ratio), calculated to normalize the morphological differences. The relative difference in muscle thickness between the two age groups was the greatest at the thigh anterior and the least at the thigh posterior in both genders. Between young men and women, the men showed significantly greater muscle thickness and Mt/Wt^1/3 ratio at every site than the women. Between the elderly groups, however, Mt/Wt^1/3 ratios at all sites, except for the thigh anterior, did not show significant gender-related differences. Relative differences in both muscle thickness and Mt/Wt^1/3 ratio between the young men and women were similar among the sites, but between the elderly groups the corresponding values at the thigh anterior were greater than at the other sites. These results indicate that 1) the influence of aging on muscle thickness differs between the muscle groups located in the anterior and posterior sited within the same segment, 2) for women, the age-related loss of muscle thickness at the thigh anterior is relatively greater as compared to those at the other sites of the lower limb.

Walking is the most basic movement in daily life, and is a popular exercise for eloerly individuals to keep their health. However, it is not clear how walking is effective in keeping or increasing the muscle mass and bone intensity of the lower limbs. This study aimed to investigate the relationships between walking steps per day during daily life and either the muscle thickness values of lower leg anterior and posterior or the bone intensity of calcaneus. The subjects were 116 healthy men (n=31) and women (n=85) aged from 60 to 78 yrs, Walking steps per day were deter-mined using a pedometer. Muscle thickness values at the lower leg anterior and posterior sites and the osteo sono assessment index (OSI) of calcaneus were determined using ultrasonographic apparatuses. In women, OSI correlated significantly with walking steps (r=0.265, p<0.05) and the product of walking steps and weight (r=0.369, p<0.05) . In both genders, however, no significant correlations were found between walking steps and muscle thickness values at the two sites. The findings here suggest that increasing the number of walking steps during daily life will improve the intensity of calcaneus for elderly women, but is not effective for inducing hypertrophic change in the muscles located in the lower limbs for elderly individuals of both genders.

This study was aimed to investigate the influences of age and gender on isometric muscle torque and explosive muscle power output with reference to muscle volume. A total of 177 healthy subjects of both genders were divided into four groups according to their age and gender : 46 young men (22.0±3.2yrs), 43 young women (22.7±3.3yrs), 46 elderly men (71.2±4.3yrs) and 42 elderly women (72.7±4.5 yrs) . The maximal voluntary isometric knee extension torque of the right leg (hip and knee angle at 90 degrees) and the power of bilateral leg extension in sitting position were mea sured. The ratios of both torque and power to muscle volume, estimated using ultrasonograph measurement, was calculated (torque/MV and power/MV respectively) . Torque was significantly less among the elderly than among the young for both genders, and among women than among the men for both age groups. Significant age-related differences were evident even in terms of torque/ MV, but the corresponding differences between men and women disappeared. On the other hand, power MV showed significant age- and gender-related differences, and the age-related difference was larger than that for torque MV. These results suggest that age- and gender-related differences in power are more noticeable than differences in torque and that these differences are not simply explained by differences in muscle volume.

According to cross-sectional studies, decreased postural stability, assessed by center of pressure (COP) sway, has been remarkable over the past 60 years, and has become one of the impairment factors for quality of life in the elderly. In the present study, in order to determine whether exercise training, consisting of bicycle ergometer and strength training inhibits decreased postural stability for elderly individuals (60 years of age or more), we investigated changes in COP sway and plantar flexors muscle volume. Healthy male (n=9) and female (n=8) subjects aged 62 to 76 yrs participated in the present study. Subjects were requested to maintain a quiet standing barefoot position on a force platform (type 9281B, Kistler) with their eyes opened or closed. Mean velocity of COP (COP sway length/time) was calculated from anterior-posterior COP sway from force platform data. From the spectral analysis of COP sway, low (0-1 Hz) and high (1 -10 Hz) frequency components of COP series were extracted. The muscle volume of the plantar flexors muscle group was estimated from multi-regression analysis based on measured muscle thickness at the lower leg posterior site using an ultrasonographic apparatus (SSD-500, Aloka) . Mean velocity of COP significantly (P< 0.05) decreased due to training, and this was accompanied by a decrease in COP sway high frequency components. On the other hand, COP sway low frequency components and muscle volume did not change. These findings suggest that an inhibition of decreased postural stability in the elderly is not mainly related to muscle volume, but to improvement of a feedback system from somatosensory function. With respect to the elderly, who have a larger mean velocity of COP, however, postural stability could be related to muscle volume.